Conventionally, international standard video encoding systems such as MPEG and ITU-TH.26x are adopted mainly on condition that an input signal format called a “4:2:0” format is used. The 4:2:0 format represents a format for converting a color image signal such as RGB into a luminance component (Y) and two chrominance components (CB and CR) and reducing the number of samples of the chrominance components to a half both in horizontal and vertical directions with respect to the number of samples of the luminance component. Since visibility for the chrominance components is low compared with that for the luminance component because of vision characteristics of the human being, the conventional international standard video encoding system is adopted on condition that an amount of information on an object of encoding is reduced by reducing the number of samples of the chrominance components before encoding is performed.
On the other hand, according to the increase in resolution and the increase in gradation of a video display in recent years, a system for encoding an image with samples identical with the luminance components without down-sampling the chrominance components is examined. A format in which the number of samples of the luminance components and the number of samples of the chrominance components are identical is called a “4:4:4” format. For an encoding system for inputting the 4:4:4: format, a “high 444 profile” is decided (see, for example, Non-patent Document 1).
While the conventional 4:2:0 format is adopted on condition that the chrominance components are down-sampled and is limited to color spaces of Y, CB, and CR, there is no distinction of a sample ratio among color components in the 4:4:4 format, so it is possible to directly use R, G, and B other than Y, CB, and CR and define and use other color spaces.
Non-patent Document 1: ISO/IEC 14496-10|ITU-TH.264 standard (Advanced Video Coding: AVC)